It could easily be caused by the water problems. And 5ppm of nitrite isn't a low reading but incredibly high. 0.25ppm is the max that fish should be allowed to be in.
The problem is that the fish tank levels are so high that 25% water changes just are not making a huge dent in it. If he has a test kit by now I would suggest do water changes all in a row until the level of nitrite gets to as close to zero as possible. That may take 5 50% water changes but it is needed right now. Once those levels get low enough then they should be easier to maintain. But each day they are growing larger and counteracting the small water change from the day before.
The problem is that the fish tank levels are so high that 25% water changes just are not making a huge dent in it. If he has a test kit by now I would suggest do water changes all in a row until the level of nitrite gets to as close to zero as possible. That may take 5 50% water changes but it is needed right now. Once those levels get low enough then they should be easier to maintain. But each day they are growing larger and counteracting the small water change from the day before.
